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United States Department of Agriculture

Agricultural Research Service

Title: Evaluation of Interspecific Competition (Aspergillus Flavus Link) and Aflatoxin Formation in Suspended Disc Culture

Authors
item Wicklow, Donald
item Bobell, John
item Palmquist, Debra

Submitted to: Aflatoxin Elimination Workshop Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: October 26, 2001
Publication Date: N/A

Technical Abstract: The ability of two non-aflatoxin producing strains of Aspergillus flavus (NRRL A-27668; NRRL 29269) to interfere with aflatoxin production by A. flavus NRRL A-27837 was examined using a replacement series with the suspended disc culture method. Individual glass fiber discs, affixed to a pin suspended from the caps of humidified 20 ml scintillation vials, were inoculated by adding 90 ul of a chemically defined salts (SL) medium containing 5% glucose and including A. flavus conidial mixtures in the following proportions (aflatoxin producer: non-producer = 100:0, 80:20, 60:40, 20:80, and 0:100) at a constant total density (1 x 10 -4 spores/ml). Reductions in the total conidial density of these strains, by dilution with sterile SL medium, had no significant effect on fungal growth (mycelium dry weight) or aflatoxin. Significant (p<0.0001) reductions in aflatoxin were recorded when NRRL A-27668 or NRRL 29269 represented any proportion of fthe inoculum mixture. Aflatoxin yield (ug/ml) values were less than expected (p<0.0001) from the input ratios for toxigenic vs. atoxigenic conidial inoculum within the replacement series. Aflatoxin yields were also reduced (p<0.001), with a corresponding increase in fungal growth (p<0.001), when conidia from pairs of the following aflatoxin producing strains, NRRL A-27837, NRRL 26473, NRRL 26474 or NRRL 26491, were mixed in equal proportions. A hypothesis is presented that vegetative incompatibility reactions prompting a compensatory growth response identified as "barrage formation" suppresses the induction of aflatoxin biosynthesis. The suspended disc culture system provides an efficient means for evaluating the outcome of A. flavus intraspecific competition on aflatoxin production in vitro.

Last Modified: 12/22/2014
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